The present invention relates generally to articles made of polymeric monofilaments, and more particularly, to methods for making brush bristles and bristle sub-assemblies, and apparatuses for making brush bristles and bristle sub-assemblies.
Brush making involves the attachment of bristles to a brush body. In one type of brush, known as the "solid block/staple set," a solid block acting as the brush body is drilled, molded, or otherwise worked to form an array of holes. Individual tufts are placed in individual holes and secured to the block by wire staples, plugs or other anchoring means. Hand drawn brushes are similar except that the tufts are secured by drawing them through the holes with an elongated strand.
Another type of brush employs a "ferrule and monofilaments" technique for attaching the bristles to the brush body. A cluster of monofilaments and cavity creating spacers are inserted into a ferrule and set with a binding resin. Ferrule brushes, such as the paint brush, are used to primarily apply liquid or viscous solutions.
In metal strip brushes, fibers are held in a "U" shaped channel of a metal strip by an anchoring wire, string, or monofilament. The channel is then crimped closed to mechanically clamp the proximal end portions of the monofilaments and anchor wire within the strip. Once formed, the brush-strips can be attached to brush bodies or otherwise shaped for specific applications.
Fused brushes are those in which polymeric tufts are fused directly to a brush body that is preferably made of the same material. One variation of fused brushes employs ultrasonic welding to secure polymeric fibers directly to a base.
With respect to the toothbrush, it is now commonplace to employ nylon monofilaments that are grouped together to form "bristle tufts." Each bristle tuft is typically arranged in a circular cluster, and a complete bristle head includes a matrix of bristle tufts arranged in rows or other patterns. The folded proximal bases of the bristle tufts are typically embedded and held in place by an anchor wire that extends across the field of the tufts and into the polymeric material that forms the head portion of the toothbrush body, while the distal ends extend upwardly therefrom, often terminating in a common plane. A more recent tufting method employs the process of cutting the tuft of monofilaments to the desired length, heat fusing the proximal ends and embedding the fused proximal ends into the polymeric material of the toothbrush head.
More recent innovations in the toothbrush art have included bristle tufts cut to provide differing lengths to provide an array of shorter and longer tufts to achieve a desired action on the user's teeth. In some tufts the monofilaments are of differing length. While these improvements can result in better functional aspects of the toothbrush, few innovations have been made over the years in techniques for manufacturing the toothbrush head; this is particularly evident in the manner in which bristles are assembled with the brush body.
In all types of known brushes, the assembly process can represent a substantial portion of the cost of manufacture since individual bristle filaments have to be held in a desired grouping and then bound to the brush body in a manner that ensures that the bristle filaments do not become detached during use. Also, recycling becomes more problematic for brushes which employ metal staples or other combinations of different classes of materials (plastics and metals, for example) in one structure. In general, the presently known techniques for forming monofilament bristle articles are not suitable for continuous feed, high through-put production, where labor requirements are relatively slight.
A machine for making pile articles useful in the field of floor coverings is described in U.S. Pat. No. 5,547,732 to Edwards et al. As seen in FIG. 1 herein, the Edwards et al. machine takes a continuous yarn 20, fed from a source 22 through a tensioner 24, and passes it through a hollow guide conduit 26 that is rotated about its center. The conduit 26 is bent to guide the yarn 20 to a position at 28 radially displaced from the center of rotation. A mandrel 30 is supported at the center of rotation and accepts the yarn 20 which is would around the mandrel 30 as it is fed from the conduit at 28.
A support strand 32 is fed into the mandrel 30 at 34 and through a passage 36 in the mandrel 30. The strand 32 exits the passage at 38 where it is guided to the outside of the mandrel 30 along ridge 40. The mandrel may have two, three, four or more such ridges where the yarn wrapping on the mandrel bends at an included angle between 0 and 180 degrees, preferably less than 90 degrees. The yarn 20 is wrapped over the strand 32 which is pulled along the mandrel 30 by a windup 41. Additional strands or yarn carriers, such as 42 and 44 propelled by motor driven pulley 46, are used to transport the yarn along the other ridges of the mandrel.
The yarn 20 is wrapped under some tension so it conforms to the mandrel 30 and is frictionally engaged with the strand and carriers for transporting before and after bonding. The wrapped yarn and strand travel together along the mandrel and under ultrasonic horn 48 where sufficient energy is imparted to the yarn that it is compacted, the multifilaments are fused together, and the yarn 20 is fused to the support strand 32. The mandrel ridge acts as an ultrasonic anvil surface. The wrapped yarn, now bonded to the strand, continues along the mandrel to cutter 50 which severs the yarn to define individual bundles of yarn having opposed ends with each bundle attached to the strand intermediate the ends.
In the aforementioned U.S. Pat. No. 5,547,732, the yarn 20 is described as a multifilament, crimped, bulky, plied-twisted yarn that has been heat set to retain the ply-twist. The yarn 20 is a thermoplastic polymer, such as nylon, polypropylene, etc. FIG. 2 shows a typical elongated pile article or tuftstring 52 made with the machine described with reference to FIG. 1. The tuftstring 52 includes a plurality of bundles of yarn 54 bent into "U" shape and attached to the support strand 32 at the inside of the "U." Each bundle defines a pair of upstanding legs or tufts 56 and 58. The tuftstrings have many advantages of manufacture in making floor coverings, and in particular, the machine produces continuous lengths of tuftstring at low cost, and with minimal labor.